The present invention relates to a control method and apparatus for producing corrugated tubing, and more particularly to a method and apparatus for producing thermoplastic corrugated tubing having a substantially uniform thickness throughout.
In the formation of corrugated thermoplastic tubing, a hollow smooth-walled extrudate is usually formed by extrusion techniques well known in the art. A corrugator immediately downstream from the extruder receives the extrudate and reforms the shape thereof by providing a corrugated configuration. Generally, the corrugator comprises continuously moving mold blocks that mate with one another to form a molding zone where the corrugating step takes place. Differential air pressure is provided to urge the extrudate into intimate engagement with the configured surfaces of the mold blocks. These blocks are configured to form alternating annular peak portions, valley portions and interconnecting side wall portions in the extrudate formed by the extruder. Unfortunately, utilization of this normal procedure produces corrugated tubing having a variable wall thickness. The overall strength and weight distribution in the finished product varies in relationship to the varying wall thickness of the product.
Utilizing normal production techniques, such as described above, the minor diameter or valley portion of the corrugation is much thicker than desired. Also, the major diameter of the tubing or peak portion together with the interconnecting side walls are thinner than desired. Hence, apparatus and procedure for thinning out the ordinarily thick valley portions of the tubing and adding to the ordinarily thin peak and side wall portions is desirable from the standpoint of a finished product of substantial uniform thickness. Stronger tubing at lighter weight is produced.